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Purpose:The aim of this study was to develop a predictive model of the shrinkage of liver tissues in microwave ablation. Methods:Thirty-seven cuboid specimens ofex vivobovine liver of size ranging from 2 cm to 8 cm were heated exploiting different techniques: 1) using a microwave oven (2.45 GHz) operated at 420 W, 500 W and 700 W for 8 to 20 min, achieving complete carbonisation of the specimens, 2) using a radiofrequency ablation apparatus (450 kHz) operated at 70 W for a time ranging from 6 to 7.5 min obtaining white coagulation of the specimens, and 3) using a microwave (2.45 GHz) ablation apparatus operated at 60 W for 10 min. Measurements of specimen dimensions, carbonised and coagulated regions were performed using a ruler with an accuracy of 1 mm. Based on the results of the first two experiments a predictive model for the contraction of liver tissue from microwave ablation was constructed and compared to the result of the third experiment. Results:For carbonised tissue, a linear contraction of 31 ± 6% was obtained independently of the heating source, power and operation time. Radiofrequency experiments determined that the average percentage linear contraction of white coagulated tissue was 12 ± 5%. The average accuracy of our model was determined to be 3 mm (5%). Conclusions:The proposed model allows the prediction of the shrinkage of liver tissues upon microwave ablation given the extension of the carbonised and coagulated zones. This may be useful in helping to predict whether sufficient tissue volume is ablated in clinical practice. [ABSTRACT FROM PUBLISHER]

Purpose:The aim of this study was to compare the performance of a microwave ablation (MWA) apparatus in preclinical and clinical settings. Materials and method:The same commercial 2.45 GHz MWA apparatus was used throughout this study. In total 108 ablations at powers ranging from 20 to 130 W and lasting from 3 to 30 min were obtained onex vivobovine liver; 28 ablations at 60 W, 80 W and 100 W lasting 5 and 10 min were then obtained in anin vivoswine model. Finally, 32 hepatocellular carcinomas (HCCs) and 19 liver metastases in 46 patients were treated percutaneously by administering 60 W for either 5 or 10 min. The treatment outcome was characterised in terms of maximum longitudinal and transversal axis of the induced ablation zone. Results:Ex vivoablation volumes increased linearly with deposited energy (r2 = 0.97), with higher sphericity obtained at lower power for longer ablation times. Larger ablations were obtained on liver metastases compared to HCCs treated with 60 W for 10 min (p < 0.003), as ablation diameters were 4.1 ± 0.6 cm for metastases and 3.7 ± 0.3 cm for HCC, with an average sphericity index of 0.70 ± 0.04. The results on thein vivoswine model at 60 W were substantially smaller than theex vivoand clinical results (either populations). No statistically significant difference was observed betweenex vivoresults at 60 W and HCC results (p > 0.08). Conclusions:For the selected MW ablation device,ex vivodata on bovine liver was more predictive of the actual clinical performance on liver malignancies than anin vivoporcine model. Equivalent MW treatments yielded a significantly different response for HCC and metastases at higher deposited energy, suggesting that outcomes are not only device-specific but must also be characterised on a tissue-by-tissue basis. [ABSTRACT FROM PUBLISHER]